1. Diagnostics of dissolved gas in insulating oil of transformers
Pekka Pietarinen

2. Contents Condition monitoring of transformers Gas formation
Gas detection
Analysis
Conclusion

3. CONDITION MONITORING METHODS
Moisture content
PD measurements
DP factor – degree of insulation degradation
Acidity
Gas analysis
Furfural analysis
Dielectric strength test (AC/impulse)
Thermal imaging

4. Condition monitoring of transformer oil
Asses the internal condition of the transformer
Assist in prediction of failures and length of lifespan
Identify faults
Detect misuse of transformers
Essential for maintenance and replacement strategies
Reduction of unplanned outages

5. Thermal fault, local hotspot
Gas formation
Two main causes of gas formation within a transformer
Oil decomposition
Mineral oil mainly composes of hydrocarbons, decomposition forms smaller hydrocarbon molecules (faults, thermal)
Different fault types produce different gases
Cellulosic degradation or decomposition
Thermal decomposition of oil-impregnated paper (cellulose) insulation H2
PD, high temperature
C2H2
Arcing
CH4
C2H4
C2H6
Thermal fault, local hotspot CO
CO2
C5 H4 O2
Paper decay

6. Detection of gases
A sample of gas has to be obtained (sample of oil or blanket gas)
Gas chromatography
Most effective way to detect gases from sample
Provides concentrations of gases from sample

7. DGA (Dissolved Gas Analysis)
The ratios of dissolved gases are used to determine the condition of the transformer or fault types
Different methods and guidelines (standards) for analysing the gas ratios are available
Key gas
IEC gas ratio
Duval triangle
Fuzzy logic
Artificial Intelligence

8. DGA (Dissolved Gas Analysis)
A chemical analysis of the contents of the gas
Not affected by electrical interference
Very inexpensive
Basically a method of comparing measured gas concentrations to existing numbers to determine results
TCG and blanket analysis

9. Diagnostics of dissolved gas in insulation oil of transformers
Different faults yield different gases
Arcing, PD, hotspots, degradation of cellulose
Gas chromatography – the most effective way to analyse gas composition
DGA
More a chemical test than electrical
Increase lifespan of transformers by redusing misuse, overload or to detect faults
Reduce damage or destruction of property
Reduce the amount of outages